Division of systems engineering

An international team led by French researchers, including those at DAp, publishes on November 28, 2023 in the Astrophysical Journal a compilation of 340 pulsars seen in gamma rays (30 MeV - 30 GeV) with the LAT space telescope on NASA's Fermi satellite.

Prior to Fermi's launch in 2008, only 11 pulsars were known in gamma rays. This new catalog brings together all the characteristics of all known gamma-ray pulsars. It contains a wealth of information on the mechanisms, poorly understood today, by which pulsar beams are generated. This wealth of centralized information will help theorists explore new avenues in their quest to understand these phenomena.

Astrophysical Journal Supplement 2023, Smith et al, The Third Fermi Large Area Telescope Catalog of Gamma-ray Pulsars

Fermi-LAT telescope continues systematic γ-ray survey

NASA's Fermi satellite was launched in June 2008, and the Fermi-LAT telescope has been carrying out a systematic γ-ray survey of near-GeV energies covering most of the sky every 3 hours (and the whole sky in no more than a week) since August 2008.

On October 9, 2022, at 13:16 and 59.99 seconds, a gamma-ray burst (GRB) dazzled almost all the X-ray and gamma ray detectors available at the time. Since their discovery, multi-wavelength telescopes in space and on the ground have continuously monitored these events. This outburst, named GRB221009A, shook the world community of astrophysicists, who have since been analysing it to understand the physical phenomena that triggered this most intense burst of energy in our history.

CEA has delivered to CNES the flight version of the ECLAIRs instrument software for the SVOM satellite. This concludes a major instrumental development phase conducted by CEA over a period of 6 years to produce what is maybe one of the most complex software packages ever carried on a French scientific space instrument. The latest version of the software equips the ECLAIRs onboard computer, which departed to China in early 2023. It will be used during the satellite integration tests in Shanghai in preparation for the launch planned for early 2024. This software will analyse in real time the data from the instrument in flight, in order to detect gamma-ray bursts and localise them to better than 12 arcmin on the sky, to reorient automatically the satellite for follow-up observations, and to alert the scientific community.

While type Ia supernovae are considered as highly symmetric supernovae, the explosion in a tight binary system composed of two white dwarfs revises this paradigm. An international team (Japan, Canada, France), including a researcher from the Department of Astrophysics/AIM Laboratory of CEA Paris-Saclay, publishes a study in the Astrophysical Journal that reveals that the distinctive asymmetric structures of such a supernova leave post-mortem imprints on the morphology of the ejected matter. These morphological signatures persist and are observable in the late phase of supernova remnants. These results open the possibility to identify and characterize the explosion scenario of this type of supernova.

The French teams of the ECLAIRs and MXT telescopes, instruments at the heart of the SVOM mission, experienced an important moment during March 2022. First, a general review of the two projects took place at CNES in Toulouse in front of a group of experts. This review allowed to verify that the two instruments meet the technical specifications and will be able to carry out the scientific mission. Then a series of team visits took place in the two CNES clean rooms housing the flight models of the two instruments, ECLAIRs and MXT.

On February 12, 2022, the ANTARES neutrino telescope (Astronomy with a Neutrino Telescope and Abyss environmental RESearch) put an end to its data taking started in 2007. During 15 years, thousands of neutrinos, precious elusive particles witnesses of the cataclysmic phenomena of the Universe, were detected at 2500 m in the Mediterranean abyss. The objective: find abnormal accumulations in the neutrino sky map revealing sources at the still mysterious origin of the cosmic rays, a rain of particles discovered more than a century ago. The CEA team played a leading role in the success of this project, a pioneer in multi-messenger astronomy.

IRFU scientists and the H.E.S.S. collaboration observe time-dependent particle acceleration in our Galaxy for the first time. Novae are powerful eruptions on the surface of a white dwarf in a binary star system, in which a larger star and a smaller star orbit each other. A nova creates a shock wave that tears through the surrounding medium, pulling particles with it and accelerating them to extreme energies. The H.E.S.S. high-energy gamma-ray observatory in Namibia has now been able to observe this acceleration process for the first time. Surprisingly, the detected nova seems to cause particles to accelerate at energies reaching the theoretical limit.

These results were published in Science: https://www.science.org/doi/10.1126/science.abn0567

The explosion of a star produces a shock wave that propagates at more than 5000 km/s for centuries and it is thought that these shocks are the main source of highly energetic particles called cosmic-rays. Studying the high-energy photon emission of supernova remnants allows us to probe the nature of the accelerated particles, their energy and their composition. A French team led by researchers from the Astrophysics division/AIM laboratory of CEA-Irfu at Paris-Saclay has confirmed the detection of gamma-ray emission above an energy of 100 MeV in the direction of the historic Kepler supernova remnant. Twelve years of observation from the LAT instrument onboard the NASA Fermi space telescope were needed to confirm the existence of an efficient particle acceleration in this remnant, one of the youngest in our Galaxy. The researchers have found that the gamma-ray emission most likely results from the interaction of accelerated ions with the surrounding medium but depending on the amplitude of the magnetic field, several scenario are plausible. This study has been accepted for publication in the journal Astronomy and Astrophysics.

After three years of reflection and development, the "Astro-Colibri" application has just been launched. This digital interface, created by researchers at Irfu/DPhP, aims to make information on transient and multi-messenger phenomena easily accessible in real time. The need to react quickly to the most violent explosions in the universe and the large amount of information provided by the global network of observatories requires new approaches and new tools. Through "Astro-Colibri", several observatories now have the capacity to coordinate in monitoring and identifying the sources of physical phenomena in the transient sky.

The platform, which exists in the form of a smartphone application (IOS and Android) and a website, allows alerts to be put into their observational context by cross-referencing them with already known data. This saves researchers a considerable amount of time. In addition, the application anticipates the best possible observation periods for a given observatory. This free interface is also a fun and practical tool for astrophysics enthusiasts who will be able to easily move around this functional application.

On June 1, 2021, the open source software solution Gammapy was selected by the CTA (Cherenkov telescope array) observatory as a high-level analysis tool (Science Tools) for the reduction and modeling of the data collected by its future network of telescopes being deployed in Chile and the Canary Islands. Gammapy benefited from the participation of some 70 scientists from all over the world with a strong involvement of German and French laboratories, including the Department of Astrophysics at Irfu (Irfu / DAp). Through contributions on analysis methods and data visualization as well as a place on the steering committee, the DAp was able to contribute to this success.

On 29 August 2019, scientists from the H.E.S.S. collaboration recorded one of the brightest cosmic explosions ever observed in the Universe. This gamma-ray burst emitted the most energetic photons ever detected in this type of event. Under the direction of Irfu researchers, the observations continued for several days. The analysis of the data collected calls into question the origin of the rays produced during the explosion. These results has been published  by the international team, which includes researchers from CEA and CNRS, in the journal Science on 4 June 2021.

H.E.S.S., located in Namibia, is a system of five imaging atmospheric Cherenkov telescopes that has been studying cosmic rays since 2003. In 2016, the cameras of the first four telescopes were completely refurbished using state-of-the-art electronics and in particular the NECTAr readout chip designed by the the DEDIP/Irfu laboratory.

The analysis of this exceptional gamma-ray burst was led by a physicist from the DPHP/Irfu astroparticle group.

An X-ray camera, intended to equip the Sino-French SVOM satellite, has just been assembled and delivered by scientists and technicians from the Institute for Research on the Fundamental Laws of the Universe (CEA/Irfu). This high-tech prototype will capture high-energy photons (X-rays) emitted during the explosion of massive stars or the fusion of dense stars. The camera, particularly compact and innovative, integrates in a very limited volume, a complete detection chain, an active thermal control and a filter wheel. It will be placed at the focus of a telescope 1.15 m long to form the MXT (Microchannel X-ray Telescope). With a field of view of 1 square degree, for only 35 kg of mass, the MXT telescope, equipped with an original "faceted" optics inspired by lobster eyes, will make it possible to locate the position of the most powerful cosmic explosions in the Universe with a precision better than 2 arcmin. After various tests, including a calibration campaign in Germany, the assembly will be shipped to China in November 2021 to be integrated into the SVOM satellite, which is scheduled for launch at the end of 2022.

See : Timelapse of the MXT camera assembling in cleanroom

Since the interferometers of the LIGO-Virgo collaboration detected gravitational waves from the merging of two black holes, black hole binaries have been among the celestial objects that most interrogate scientists. A team of astronomers, including researchers from the Astrophysics Department / AIM Laboratory of CEA Paris-Saclay and the APC laboratory (University of Paris), have determined, using more than 60,000 digital simulations of stellar evolution, the characteristics of the progenitors at the origin of mergers of black hole binaries of mass less than 10 solar masses. According to this study, a phase in the evolution of the binary system known as the common envelope phase plays an essential role in the process eventually leading, or not, to the merger of the two black holes. This work is presented in an article to appear in the journal Astronomy & Astrophysics.

An international campaign including ground-based and space telescopes, including the INTEGRAL satellite, discovered end of April 2020 very short pulses in both X-rays and radio waves coming from a compact object in the Galaxy, the magnetar SGR 1935+2154. The simultaneous observation of these signals is seen for the first time in this type of source and attests a connection between magnetars and Fast radio bursts, a class of radio sources whose origin is today poorly known. This work, that includes researchers from the Astrophysics Department/ AIM Laboratory of CEA-Irfu of Paris-Saclay, is published in The Astrophysical Journal Letters and subject press release of a European Space Agency (ESA).

An international team, led by astronomers from Cardiff University, with the contribution of the Astrophysics Department of CEA-Irfu, may have spotted for the first time the compact remains of the last star explosion visible by eye that occurred on February 23, 1987 in a nearby galaxy, the Large Magellanic Cloud, only 160 000 light-years away.
Using the high-resolution images of the ALMA radio telescope in the Atacama Desert in northern Chile, the team discovered a small area of dust, warmer than its environment, which may correspond to the supposed location of the compact neutron star that should have formed during the explosion according to theoretical models. This compact object had been searched without success for more than 30 years. This indirect discovery nevertheless requires to be confirmed by additional data. These results are published in The Astrophysical Journal.

After a decade-long search, scientists have for the first time detected a gamma-ray burst in very-high-energy gamma light. This discovery was made in July 2018 by the H.E.S.S. collaboration using the  huge 28-m telescope of the H.E.S.S. array in Namibia. Surprisingly, this Gamma-ray burst, an extremely energetic flash following a cosmological cataclysm, was found to emit very-high-energy gamma-rays long after the initial explosion. This discovery was published in Nature.

The first results of the space mission SVOM (for Space-based multi-band astronomical Variable Objects Monitor) have just fallen before the launch scheduled for the end of 2021. How is this possible? Quite simply because this ambitious Franco-Chinese mission, which aims at studying gamma-ray bursts of the Universe, is also developing a network of ground-based cameras able to detect the emission of visible light that follows the outbreak of these bursts, the most violent known explosions. This network, dubbed Ground-based Wide Angle Camera (GWAC), is already in operation at the Xinglong Observatory in Northeast Beijing (China). Its test version, dubbed Mini-GWAC, successfully concluded a first campaign of monitoring and real-time follow-up of gravitational wave sources discovered by the LIGO (USA) and Virgo (Italy) facilities. These results are being published in the journal Research in Astronomy and Astrophysics.

Thanks to the X-ray satellites Chandra and XMM-Newton, an international team including the Department of Astrophysics of CEA-Irfu has just discovered the existence of two bubbles of hot gas escaping to distances of about 500 light-years, on both sides of the massive black hole environment, in the center of our galaxy. Like the messages of Native Americans transmitted by smoke bubbles visible from afar, these "hot gas chimneys" tell us today about the intense past activity of the black hole and the central regions of our Galaxy. These results are published in the journal Nature of March 21, 2019.

Despite a short period of activity, the japanese space agency (Jaxa) Hitomi satellite has shown its full potential by delivering relevant information’s on several celestial objects. In a series of works based on these observations and gathered in an issue of the review Publications of the Astronomical Society of Japan (PASJ), the Hitomi collaboration (among it researchers from the Astrophysical Department of CEA-Irfu Saclay) presents results that take advantage of the exceptional spectral resolution of the SXS spectrometer, one of the payload instrument. At the heart of this work is a detailed study of the dynamics of plasma in the center of an active galactic nucleus, of the ejecta of several supernova remnants, of the composition of matter in a binary system or the search for X and radio correlations in the Crab pulsar thanks to the high temporal resolution. Performed during the verification and calibration phase of the instruments before the satellite failed, these observations and the quality of the results confirm the community's choice on the instruments and the high potential of the high resolution X-rays spectroscopy. The Hitomi team is currently preparing its successor, Xrism (X-Ray Imaging and Spectroscopy Mission) and ESA is on its side working on the Athena project, a major X-rays observatory in which CEA is deeply involved

Read more in : Haute résolution pour le satellite Hitomi (in French)

A prototype of the MXT camera arrived at the CNES in Toulouse on 25 October 2018. This is the Structural and Thermal Model (STM), which will be integrated into the telescope that will be sent to China to be mounted on the SVOM satellite Qualification Model.

The objective of this model is to validate the thermo-mechanical design of the camera. It also makes it possible to check the manufacturing and assembly capacity of the various components, which represent more than 1,000 elements. The model realized includes all the camera subassemblies with a good level of representativeness of the flight model, both on its external design (interfaces with the telescope) and on its internal design (harnesses, connectors...). The electrical parts (detector, electronic boards, motor) are replaced by weights and heaters to simulate their mechanical and thermal behaviour. 

X-ray photons were detected for the first time in late August 2018 with an engineering model of the SVOM MXT focal plane. This is an important step towards the validation of the design of the detection chain.
The MXT telescope, for Microchannel X-ray Telescope, will be flown on board the SVOM satellite, a collaborative project between France (CNES) and China (CAS, CNSA) to study gamma-ray bursts. It aims at detecting soft X-rays (0.2 to 10 keV) at during the early phases of the afterglow emission, and at providing an accurate (smaller than 1 arc minute) position of the burst. Irfu is in charge of the design and realization of the telescope camera, integrating a pnCCD (provided by MPE) X-ray imaging spectrometer assembled on a dedicated ceramic board. The flight model of the detector must be integrated into the camera in one year from now.

A hundred years old mystery might get resolved with the detection of neutrinos by the IceCube collaboration coming from a known active black hole. Irfu, which coordinate those observations with the H.E.S.S. telescope, did not detect anything for now but the multi-messenger astronomy has just begun…

On May 7, 2018, the European Space Agency (ESA) announced the three selected space missions, out of the 25 proposed, for the fifth ESA middle class mission in its scientific program Cosmic Vision, whose launch date is planned in 2032. One of these three missions is the THESEUS project (Transient High-Energy Sky and Early Universe Surveyor), a project developed in recent years by a large European consortium in which the Astrophysics Department-AIM Laboratory of CEA-Irfu plays a major role. THESEUS aims to explore the early Universe (the first billion years) through gamma ray bursts (GRBs), the most extreme explosions of the cosmos, and to provide accurate detection, localization, and distance measurement of gravitational waves and neutrinos sources, as well as many other transient celestial sources.

The birth spin of a neutron star is a key parameter to better understand the nature of its progenitor as well as the dynamical processes at play during the collapse of a massive star. However, the distribution of initial pulsar spins is poorly known. A study led by R. Kazeroni from SAP/CEA and his collaborators, using numerical simulations, emphasized the efficiency of a hydrodynamic instability named “SASI” to impart a rotational velocity to the neutron star. Surprisingly, the simulations show that, in some cases, the direction of rotation of the compact object is opposite to the perturbation which triggers the rotation. These results are published in the journal Monthly Notices of the Royal Astronomical Society.

A team of researchers from CEA (Astrophysical Department and CEA-DAM) and the LUTH Laboratory (Paris Observatory) has just published a comprehensive study of an enigmatic phenomenon of quasi-periodic oscillations at the surface of strongly magnetic white dwarfs also called "Polars ". These dense stars are orbiting a companion and capture its material that falls freely toward the white dwarf poles. Strongly heated to millions of degrees, the hot gas or plasma then emits mainly in X-rays. Thanks to detailed numerical simulations of the plasma behavior, the researchers were able to reconstruct the existence of strong instabilities leading to rapid oscillations in the luminosity with timescales of only a few seconds. However, using the database of the XMM-Newton satellite, these oscillations were sought unsuccessfully by the team, in the X-ray emission of over 20 Polars. This contradiction leads today researchers to propose to study the phenomenon in the laboratory. Indeed, similar physical conditions can currently be replicated by large power lasers like the LMJ [1]. The control of plasma instabilities is a key element for nuclear fusion by magnetic (ITER experience) ou inertiel confinement (laser Mégajoule) and instabilities of white dwarfs could contribute to a better understanding of this general phenomenon. These results are the subject of two articles published in the journal Astronomy & Astrophysics, July 2015.

see the movie of the numerical simulation (short version)

2014 has been a fruitful year for SVOM (Space-based multiband astronomical Variable Objects Monitor), a chinese and french space mission dedicated to the study of gamma-ray bursts. The decisions taken at the highest level, the governments in March and the respective space agencies in August, restart the project after a frozen period. As a direct result, two important meetings of the consortium (kick-off meeting) took place in September, one at CNES in Toulouse and the other at Shanghai. These meetings mainly based on technical aspects of the project are an important step towards the realization of the satellite payload of the mission which is scheduled to be launched in 2021. CEA-IRFU and its Astrophysics Department play a major role in this project in partnership with CNRS and under the overall responsibility of CNES.

For a more detailed account, see the French version.

The central black hole of the Galaxy, today surprisingly quiet, has undergone, several hundred years ago, a violent phase of activity. This is the conclusion reached by an international team led by astrophysicists of the APC laboratory and including scientists of the Service d'Astrophysique of CEA-Irfu, by studying the high energy emission of molecular clouds located in the central regions of the Galaxy. The scientists have indeed discovered complex variations of this emission, with some of them showing propagation velocity greater than the speed of light. They reveal that a giant outburst, most probably generated by the black hole, took place about 400 years ago. The powerful flare is visible today after reflection by the molecular clouds that play the role of celestial mirrors. The recent history of the region retraced in this way shows that the black hole of the galactic centre is not so different from the supermassive black holes of the active galactic nuclei. This work, based on two long term observing programs of the XMM-Newton and Integral satellites, is the object of two complementary publications in  The Astrophysical Journal.

Surprisingly, an asymmetry in the distribution of antimatter in the central regions of our Galaxy has just been discovered. By adding all scientific data acquired since five years by the spectrometer SPI aboard the INTEGRAL satellite, a European research group, including scientists from the Service d'Astrophysique at CEA-IRFU , has observed a gamma-ray photon emission of an energy of 511 keV, which is characteristic for the annihilation of electrons and their antimatter particles, the positrons. The researchers could determine the morphology of the 511 keV emission in the central regions of our Galactic disk, which reveals to be asymmetric and very similar to the distribution of a certain type of X-ray binary sources. For some time already these objects are thought to be efficient factories for positron production, and could explain the origin of these antimatter particles in the central regions of our Galactic disk. This work has been published in the scientific journal Nature on January 10th, 2008.